1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine.
2. Description of Related Art
Conventionally, an internal combustion engine, in which an exhaust gas control catalyst is provided in an exhaust passage of the internal combustion engine, an air-fuel ratio sensor is provided on an upstream side of this exhaust gas c catalyst in an exhaust gas flow direction, and an oxygen sensor is provided on a downstream side of this exhaust gas control catalyst in the exhaust gas flow direction, has widely been known. A control apparatus for such an internal combustion engine controls an amount of fuel supplied to the internal combustion engine on the basis of output of each of these air-fuel ratio sensor and oxygen sensor.
As the control apparatus for such an internal combustion engine, for example, one that executes the following control has been known. When the output of the oxygen sensor is reversed from a value indicative of a richer air-fuel ratio (hereinafter, referred to as a “rich air-fuel ratio”) than a theoretical air-fuel ratio to a value indicative of a leaner air-fuel ratio (hereinafter, referred to as a “lean air-fuel ratio”) than the theoretical air-fuel ratio, a target air-fuel ratio of the exhaust gas that flows into the exhaust gas control catalyst is set at the rich air-fuel ratio. On the other hand, when the output of the oxygen sensor is reversed from the value indicative of the lean air-fuel ratio to the value indicative of the rich air-fuel ratio, the target air-fuel ratio is set at the lean air-fuel ratio (for example, Japanese Patent Application Publication No. 2008-075495 (JP 2008-075495 A)).
In particular, in the control apparatus described in JP 2008-075495 A, a deviation integration value is calculated by integrating a value that corresponds to a deviation between the output value of the oxygen sensor and a reference value corresponding to the target air-fuel ratio. In addition, the air-fuel ratio is controlled on the basis of the thus-calculated deviation integration value such that the air-fuel ratio of the exhaust gas flowing into the exhaust gas control catalyst corresponds to the target air-fuel ratio. Then, in the case where the output of the oxygen sensor is not reversed again even after a specified period has elapsed since the reversal of the output of the oxygen sensor, a learned value is corrected. According to JP 2008-075495 A, due to the above control, even when the learned value is largely deviated from an appropriate value, it can promptly be converged to the appropriate value.